In particular, the invention relates to a method and an apparatus adapted to be used for positioning the photosensitive substrate in a direction of rotation in an exposure apparatus (a stepper, an aligner and the like) for producing a semiconductor device, a charge coupled device (CCD), a liquid crystal indication element, a thin film magnetic head and the like.
In a projection exposure apparatus such as a stepper and the like which is used in manufacturing a semiconductor device, a liquid crystal indication element and the like, it is desired to position (or align) with high accuracy a reticle which constitutes a mask with a wafer (or a glass mask and the like) which constitutes a photosensitive substrate, in order to transfer a circuit pattern formed on the reticle onto a photoresist layer on the wafer with high alignment accuracy.
There are various types of alignment sensors used in the alignment system, one of which is an LSA (Laser Step Alignment) type, such as shown in Japanese Patent Laid-Open Publication No. Hei 5-21324, in which a laser beam is irradiated to a doted-line-shaped alignment mark on a wafer and the position of the alignment mark is detected on the basis of the beam diffracted or scattered by the mark, another is an FIA (Field Image Alignment) type in which an image of an alignment mark is taken by illuminating with the light having a wide wave band width and emitted from a halogen lamp as a light source and the position of the alignment mark is measured by image-processing the obtained image data, and yet another is an LIA (Laser Interferometric Alignment) type in which a diffraction grating-shaped alignment mark on a wafer is irradiated from two different directions with two laser beams having slightly different frequencies with each other, and two diffracted beams emitted thereby interfere with each other to thereby enable the position of the alignment mark to be measured using the phase between the two diffracted beams. Alignment systems can be roughly divided into a TTL (Through-The-Lens) type in which the position of a wafer is detected through an optical projection system, a TTR (Through-The-Reticle) type in which a positional relationship between a reticle and a wafer is measured through an optical projection system and the reticle, and an Off-Axis type in which the position of a wafer is directly detected without using an optical projection system.
The position of a wafer not only in a translational direction and but also in a direction of rotation (angle of rotation) is detected by detecting the positions of at least two points on a wafer placed on a wafer stage by means of these alignment sensors. There are several alignment sensors such as a TTL and LIA (Laser Interferometric Alignment) type, and a TTL and LSA (Laser Step Alignment) type and an Off-Axis and FIA (Field Image Alignment) type as a sensor used in measuring an angle of rotation of the wafer.
For the projection exposure apparatuses, it is desired to align a reticle and a wafer with high accuracy based on detected results by these alignment sensors while reducing the time required for effecting an alignment of the reticle and the wafer and maintaining a high productivity (throughput). Therefore, it is necessary to increase productivity in all steps from a step in which a wafer is transferred to a wafer stage to the final exposure step. Referring to FIG. 1, the operation in a transfer process of a wafer prior to the final alignment of the wafer in the conventional exposure apparatus will be explained, hereinafter.
FIG. 1 shows a structure around a wafer stage explaining a transfer mechanism for a wafer in a conventional exposure apparatus. In FIG. 1, a state in which a substrate or wafer W is transferred from a wafer carrier device onto an elevating or vertically movable device g disposed through a telescoping mechanism f on an X stage a. The elevating device g includes three supporting pins (in FIG. 1, two supporting pins g1 and g2 are shown) which are loosely inserted into openings formed in each of a sample table c, a xcex8 rotation correction mechanism d and a wafer holder e with play therebetween. The elevating device operates such that three supporting pins thereof moves the wafer W up and down by upward and downward movement of the telescoping mechanism in response to a transfer operation of the wafer. Each supporting pin g1, g2 or g3 is adapted to suck the lower surface of the wafer by vacuum suction generated by an external vacuum pump to hold the wafer so that it does not move or displace when the elevating device is moved up and down.
After the wafer W is stationarily held on the wafer holder e by vacuum suction, the alignment sensor generates a detection signal of alignment marks formed on the opposite ends of the wafer W and a rotational error or angular error on a coordinate system of the wafer stage is calculated by obtaining the coordinates of the sample table c, for example, when a detected signal reaches its peak and is measured by means of a movable mirror h fixed on the end of the sample table c and an external interferometer (not shown). The rotational error of the wafer W is eliminated by driving the xcex8 rotation correction mechanism (xcex8 table) d on the sample table e based on the obtained results, thereby carrying out alignment of the reticle and the wafer W in the direction of rotation.
In the prior art as explained above, the xcex8 rotation correction mechanism d for rotating the wafer is provided between the wafer W and the sample table e which is a reference of the coordinate system of the wafer stage system and is provided with the movable mirror h thereon. This results in some inconveniences that the wafer W is displaced in a lateral direction when vacuum suction of the wafer holder for holding the wafer W is weak, that the rigidity of the entire stage becomes weak since complex mechanisms are provided on the sample table c and that the control performance of the stage cannot be increased since the weight of the entire stage increases. Therefore, it may be intended, for example, that the xcex8 rotation correction mechanism is arranged below the sample table c. In this case, however, angle of rotation of the xcex8 rotation correction mechanism is limited when the xcex8 rotation correction mechanism is driven to adjust the angle of rotation of the wafer W, since the angle of a light beam from the laser interferometer which strikes the movable mirror h on the sample table c varies. Therefore, for example, if accuracy of pre-alignment of the wafer is not good, the rotational error cannot be sufficiently corrected.
Also in the prior arts, when an alignment sensor of a diffracted light detection type such as the LAS type or the LIA type, particular detection errors are created in response to an angle of inclination between an alignment mark on a wafer W and the light beam for detecting a position.
FIGS. 2(a) and 2(b) illustrate a state in which laser beam is irradiated to an alignment mark. FIG. 2(a) shows a state in which an alignment mark (grating-shaped) for the LIA type is irradiated with a laser beam and FIG. 2(b) shows a state in which an alignment mark (doted-line-shaped mark) for the LSA type is irradiated with a laser beam. As shown in FIG. 2(a), in the alignment system of the LIA type, a grating-shaped alignment mark is irradiated from two directions with two laser beams each having a rectangular irradiation region and the wafer is positioned on the basis of a phase of the interfered light of two diffracted lights form the alignment marks. In FIG. 2(a), an irradiation region RA1 of the laser beam is inclined by xcex94xcex8A with respect to a central axis GMy extending along a longitudinal direction (non-measuring direction) of a grating-shaped mark GM which is formed by a plurality of gratings arranged with a predetermined pitch in a right and left direction.
Also, as shown in FIG. 2(b), in the alignment system of the LSA type, a dotted-line-shaped mark DM formed from a plurality of small square patterns arranged in an upward and downward direction with a predetermined pitch is scanned with a laser beam which is condensed at a slit-shaped irradiation region RA2y and the position at which a quantity of an interfered light form the marks becomes maximum is detected. In FIG. 2(b), a central axis DMy extending along a longitudinal direction of a slit-shaped irradiation region RA2 of the laser beam is inclined by xcex94xcex8B with respect to a central axis DMy extending along the direction of arrangement (non-measuring direction) of the doted-line-shaped mark DM.
Therefore, in both cases shown in FIGS. 2(a) and 2(b), it may occur that positional detection errors are created due to an angle of inclination between the alignment mark and the laser beam. That is, since photoresist is applied on the alignment mark, if a difference in intensity of the diffracted beam returned from the alignment mark is created due to a difference in film thickness of the photoresist which depends on difference in position in the non-measuring direction of the mark, the position of the mark is detected such that it is shifted toward a side where the intensity of the returned light is great. Therefore, the detected error by the LIA system shown in FIG. 2(a) becomes L3xc3x97xcex94xcex8A in maximum which is a product of the length L3 of the grating-shaped mark GM in a longitudinal direction thereof and an angle xcex94xcex8A. On the other hand, the detection error by the LSA system shown in FIG. 2(b) becomes L4xc3x97xcex94xcex8B in maximum which is a product of the length L4 of the dotted-line-shaped mark DM and the angle xcex94xcex8B. However, according to prior arts these detection error cannot be deleted easily.
On the other hand, there is a known positioning or aligning apparatus which, when a wafer is placed on an exposure or substrate stage, detects the position of an outer peripheral edge of the wafer without contacting the wafer and positions the wafer on a substrate stage so that it is placed at a predetermined position on the substrate stage and an orientation-flat (hereinafter refer to as xe2x80x9cflatxe2x80x9d) becomes parallel with a direction of movement of the substrate stage (for example, the direction X).
Such a prior art apparatus for positioning the wafer with respect to the exposure stage in the non-contact way is disclosed, for example, in Japanese Patent Laid-Open Publication No. Sho 63-280435. According to this prior art apparatus, the wafer is put on a rotary table of a pre-alignment device provided adjacent to the exposure stage, a peripheral configuration of the wafer is photoelectrically detected as the wafer is rotated. Next the position of the wafer and the direction of the flat formed on the wafer are compensated so that they are at the predetermined position and direction, before the wafer is mounted on the exposure stage. Thereafter, the wafer is carried from the pre-alignment device to the exposure stage by means of a carrier arm keeping its"" posture as it is, whereby the wafer is positioned in the predetermined place on the exposure stage so that the direction of the flat is parallel with one (X direction) of the moving directions of the exposure stage. In the wafer positioned on the exposure stage by the positioning apparatus as mentioned above, however, the position thereof with respect to the exposure stage and parallelism of the flat with respect to the X direction become disordered and the position and the parallelism become uneven wafer by wafer with respect to the exposure stage during two transfer operations of wafer W, that is, when the wafer is transferred from the pre-alignment device to a carrier arm and when it is transferred from the carrier arm to an exposure stage.
On the other hand, there is disclosed in Japanese Patent Laid-Open Publication No. Sho 63-107139 a method for detecting the position of a wafer and the direction of the flat with respect to the X direction in order to effect the pre-alignment of the wafer more precisely after the wafer, the position of which and the direction of the flat are compensated by the pre-alignment described above, is mounted on the exposure stage. This method uses a laser beam irradiating an alignment mark on the wafer when fine alignment (a precise position alignment between the wafer and a projected image of a circuit pattern) is performed, scanning two separated points on the flat portion of the wafer held on the stage and two points on the circular peripheral edge of the wafer by the laser beam, thereby obtaining a rotational error (an offset in the direction of rotation of the wafer) of the flat with respect to said one moving direction (X direction) of the stage and X-Y coordinate positions. After this the direction of the flat formed on wafer coincides with the X direction by rotation of a wafer holder holding the wafer on the basis of the rotational errors.
As shown in U.S. Pat. Nos. 4,407,627 and 4,345,836, there has been proposed a structure which performs a more precise pre-alignment by providing a second pre-alignment mechanism wherein the wafer, the position of which and the direction of the flat formed on which are compensated is mechanically pushed against a positioning pin or pins provided on the exposure stage, after the wafer are placed thereon.
However, when the positioning of the wafer is performed by using the laser beam for a fine-alignment, a plurality of measurement points on the periphery of the wafer should be moved to the irradiation position where the laser beam is irradiated on the wafer. This results in an increase of displacement of the exposure stage and reduction of a throughput.
On the other hand, when the pre-alignment is performed by making the second pre-alignment mechanism mechanically contact with the periphery of the wafer, contaminants such as photoresist or the like attached to the wafer are scattered within the apparatus and on the wafer, thereby preventing improvement in an yield rate of semiconductor chips. Moreover, since the pre-alignment mechanism provided outside the apparatus and a carrier arm for carrying the wafer from the outside pre-alignment mechanism to the exposure stage are the same as those of the apparatus having no second pre-alignment mechanism, it is difficult to improve positioning accuracy.
The main object of the present invention is to provide a positioning method and apparatus which is capable of eliminating detection errors caused by an angular error between a light beam of an alignment sensor of diffracted light detection type and an alignment mark to position a substrate such as wafer or the like with high accuracy.
Another object of the present invention is to provide a positioning method in which the structure of a substrate stage is simplified to thereby enabling improvement in rigidity of the substrate stage and decrease of weight thereof, and, as a result, positioning of the substrate can be performed rapidly and with high accuracy.
A further object of the present invention is to provide a positioning method in which a band-shaped light beam is irradiated to a mark formed on a substrate to detect the position of the substrate with respect to a substrate stage and measure mutual relation between the direction of the band-shaped light beam and the direction of the substrate stage, and in which the substrate is positioned with low cost by moving a mask pattern and the substrate on the basis of the measured results.
A further object of the present invention is to provide a positioning method in which an angular error of a substrate relative to a predetermined two dimensional coordinate system is obtained and the angular error is corrected by relatively rotating the substrate with respect to a substrate holder of a substrate stage, thereby quickly performing positioning of the substrate to improve throughput of the apparatus.
A further object of the present invention is to provide an aligning method for aligning a substrate held on a substrate stage which is movable in a predetermined direction with a mask pattern on a mask.
A yet another object of the present invention is to provide a positioning apparatus for a substrate which is capable of positioning the substrate such as a wafer or etc. with respect to a stage capable of moving in two dimensions, without decreasing throughput of the apparatus.
A yet another object of the present invention is to provide a positioning apparatus for positioning a substrate so that a straight or flat portion (a flat) on the periphery of the substrate is always oriented toward a predetermined direction with respect to a holder for holding the substrate.
A yet another object of the present invention is to provide a positioning apparatus for a substrate which is capable of positioning the substrate rapidly and with high accuracy by detecting a straight or flat portion of the substrate without contacting the wafer while the substrate is in the position on the holder.
A yet another object of the present invention is to provide a positioning apparatus for positioning a substrate so that a straight or flat portion on the periphery of the substrate is always oriented toward a predetermined reference position with respect to a holder when the position of the holder in the direction of rotation is in a neutral position.
A first positioning method according to the present invention relates to a method for positioning a substrate on a substrate stage which is movable in a predetermined direction (Y direction) and includes steps of measuring a relationship between a longitudinal direction (Xxe2x80x2 direction) of a band-shaped light beam irradiated onto said substrate and said predetermined direction (Y direction) to detect the position of said substrate in said predetermined direction; and positioning said substrate on said substrate stage based on the relationship between said longitudinal direction of said band-shaped light beam and said predetermined direction.
In this case, it is preferable to position the substrate on the substrate stage based on the relation between a longitudinal direction of the band-shaped light beam and the predetermined direction.
A second positioning method according to the present invention relates to a method for positioning a substrate on a substrate holder on the basis of a predetermined two dimensional coordinate system and includes steps of obtaining a rotational error of the substrate placed on the substrate holder with respect to said two dimensional coordinate system; and taking out said substrate from said substrate holder and then rotating said substrate so that said rotational error is corrected, thereafter placing again said substrate onto said substrate holder.
In this case, preferably, a minute rotational or angular error of the substrate with respect to the two dimensional coordinate system may be measured after the rotational error of the substrate is corrected and then a mask pattern may be rotated so that the minute rotational error is corrected.
A third positioning method according to the present invention relates to a method for positioning a substrate having a straight section formed at a part of the outer periphery thereof with respect to a substrate holder which is rotatably disposed on a two dimensionally movable substrate stage and has a flat section formed at a part of the outer periphery thereof and includes steps of moving a roughly pre-aligned substrate to a position above said substrate holder; irradiating parallel light beams from above the substrate holder to at least two portions on said flat section and at least one portion on another outer periphery toward said substrate holder; measuring quantity of light reached said substrate holder by means of sensors to obtain an angular error of said substrate relative to said substrate holder; rotating the substrate holder relative to said substrate by an angle equal to the obtained angular error; and rotating the substrate holder in the opposite direction by said angle after the substrate is placed on the substrate holder.
A forth positioning method according to the present invention relates to a method for positioning a substrate having a straight section formed at a part of the outer periphery thereof with respect to a substrate holder which is rotatably disposed on a two dimensionally movable substrate stage and has a flat section formed at a part of the outer periphery thereof and includes steps of moving a roughly pre-aligned substrate to a position above the substrate holder; irradiating parallel light beams from above said substrate holder to at least two portions on said flat section and at least one portion on another outer periphery toward the substrate holder; measuring the quantity of light which reaches said substrate holder by means of sensors to obtain an angular error of said substrate relative to said substrate holder; and placing said substrate onto said substrate holder after said substrate is relatively rotated with respect to the substrate holder by an angle equal to the angular error.
A first aligning method according to the present invention relates to a method for aligning a substrate held on a substrate stage which is movable in a predetermined direction with a mask pattern on a mask and includes steps of measuring a relationship between a longitudinal direction of a band-shaped light beam and said predetermined direction to detect the position of said substrate in said predetermined direction; and aligning said mask and said substrate with each other based on said relationship between said longitudinal direction of said band-shaped light beam and said predetermined direction.
A second aligning method according to the present invention relates to a method for aligning a substrate held on a substrate stage with a pattern on a mask based on a predetermined two dimensional coordinate system and includes steps of obtaining a rotational error of said substrate placed on said substrate holder relative to said two dimensional coordinate system; separating said substrate from said substrate holder and then rotating said substrate to correct said rotational error; thereafter placing again said substrate on said substrate holder; measuring a minute rotational error of said substrate with respect to said two dimensional coordinate system after said correction of said rotational error of said substrate finished; and rotating said mask to correct said minute rotational error.
According to the positioning or aligning method of the present invention as explained above, as shown in FIG. 6(a), an angle of rotation xcex8LSAY of a longitudinal direction (Xxe2x80x2 direction) of a band-shaped light beam from an alignment sensor relative to a coordinate system of the substrate stage, and, for example, a mask pattern and a substrate is rotated by the angle of rotation xcex8LSAY with respect to a predetermined direction of movement of the substrate stage. Since the substrate is rotated in correspondence with the direction of the band-shaped light beam from the alignment sensor, the rotational error between the band-shaped light beam and the substrate is removed by an alignment and positional detection error is removed.
Moreover, when the substrate is positioned on the substrate stage in consideration of a relation between the longitudinal direction of the band-shaped light beam and the predetermined direction, the rotational error between a mark on the substrate on the substrate stage and the band-shaped light beam from the alignment sensor is reduced.
According to the other positioning or aligning methods of the present invention, since a rotational error (xcex94xcex8N) of the substrate relative to a predetermined coordinate system is obtained and the substrate is separated from the substrate holder, thereafter, the substrate is rotated so that the rotational error is corrected, the substrate is placed on a substrate holder, no rotation correction mechanism is required for a substrate stage. Therefore, the substrate stage is improved in rigidity and its weight is reduced.
Further, if a minute rotational error in the substrate relative to a two dimensional coordinate system is measured after a rotational error of the substrate is corrected and a mask pattern is rotated so that the minute rotational error is corrected, alignment of the substrate in a rotational direction is rapidly performed without providing a mechanism for correcting the minute rotational error, for example, for the substrate stage.
A first positioning apparatus according to the present invention relates to an apparatus for positioning a substrate on a substrate stage which is movable in a predetermined direction and comprises a reference mark member mounted on said substrate stage and having a reference mark formed thereon; an alignment sensor which is capable of selectively irradiating a band-shaped light beam onto said reference mark member and said substrate placed on said substrate stage; an elevating base which is disposed above said substrate stage and is vertically movable and rotatable independently from said substrate stage to receive said substrate transferred to a position above said substrate stage and place it on said substrate stage; and a drive mechanism for vertically moving and rotating said elevating base.
Another positioning apparatus for a substrate according to the present invention includes a stage two dimensionally movable in a predetermined reference plane; a holder for holding a substrate having a straight portion on at least a part of the periphery thereof; a holding member for holding the substrate above the stage in a parallel relationship with respect to the reference plane, when the stage is in the reference plane; a rotational error detecting device for detecting a relative rotational error of the straight portion of the substrate with respect to a reference direction on the basis of electric signals, said detecting device having irradiation elements each of which irradiates a beam of light to the straight portion of the substrate held by the holding member and an optical detecting elements each of which optically detects the beam of light on the opposite side from the irradiation device with respect to the substrate and outputs said electric signal; and a rotary drive device for rotating one of the substrates and holders.
A further positioning apparatus for a substrate according to the present invention includes a stage two dimensionally movable in a predetermined reference plane; a holder for holding a substrate having a straight portion on at least a part of the periphery thereof; a holding member for holding the substrate above the stage in a parallel relationship with respect to the reference plane, when the stage is in the reference plane; a rotational error detecting device for detecting a relative rotational error of the straight portion of the substrate with respect to a reference direction on the basis of electric signals, said detecting device having irradiation elements each of which irradiates a beam of light to the straight portion of the substrate held by the holding member and an optical detecting elements each of which optically detects the beam of light on the opposite side from the irradiation device with respect to the substrate and outputs said electric signal, one of said irradiation elements and optical detecting elements being disposed on the holder; and a rotary drive device for rotating the holder by a value corresponding to the rotational error between a position of the holder in the direction of rotation and a neutral position, whereby the substrate is mounted on the holder so that the straight portion of the substrate held on the holder becomes substantially parallel with the predetermined reference direction when the position of the holder in the direction of rotation is in the predetermined neutral position.
In one embodiment of the above positioning apparatus, the optical detecting elements of the apparatus may be disposed on the holder, and the rotary drive device may include a controller controlling rotation of the holder so that the electric signals from the optical detecting elements become predetermined reference values, respectively.
A further positioning apparatus for a substrate according to the present invention includes a stage two dimensionally movable in a predetermined reference plane; a holder for holding a substrate having a straight portion on at least a part of the periphery thereof; a holding member for holding the substrate above the stage in a parallel relationship with respect to the reference plane, when the stage is in the reference plane; a rotational error detecting device for detecting a relative rotational error of the straight portion of the substrate with respect to a reference direction on the basis of electric signals, said detecting device having irradiation elements each of which irradiates a beam of light to the straight portion of the substrate held by the holding member and an optical detecting elements each of which optically detects the beam of light on the opposite side from the irradiation device with respect to the substrate and outputs said electric signal, one of said irradiation elements and optical detecting elements being disposed on the holder; and a rotary drive device for rotating the substrate so that the rotational error becomes zero, whereby the substrate is mounted on the holder so that the straight portion of the substrate becomes substantially parallel with the predetermined reference direction.
In another embodiment of the above positioning apparatus, the optical detecting elements of the apparatus may be disposed on the holder, and the substrate rotary drive device may include a controller for controlling the rotation of the holder so that the photoelectric signals from the photoelectric detecting elements become predetermined reference values, respectively.
According to the present invention, the substrate is held above the stage disposed in a predetermined position (transfer position) before the substrate is mounted on the holder and the rotation error or angular offset of the straight portion (flat) of the substrate with respect to the reference direction (or reference line) is detected by the rotation error detecting device. The substrate is mounted on the holder after the rotary drive device rotates, for example, the holder from the neutral position by a value corresponding to the rotation error. Then it is possible to position the substrate on the stage by rotating the holder back to the neutral position so that the direction of the straight portion of the substrate and the reference direction become substantially parallel.